Just How Good is the Sigma BF’s Autofocus Tech?

Apr 16, 2026

Chris Niccolls

It started with an offhand question during a casual conversation: Can the Sigma BF autofocus keep up with the demands of wildlife and sports photography?

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Obviously, the Sigma BF design with its sharp edges and tiny body is woefully inequipped to handle large lenses. But the tracking autofocus blew us away with how sticky and capable it was when we first tested it, and this unsolved mystery would not go away. To be fair, I was only testing it as a street and travel camera, a situation where it nailed focus adroitly, but we all wondered if it could handle something more demanding?

I mounted the excellent Sigma 300-600mm f/4 DG OS Sports lens to two cameras for this test: the Sigma BF, which was awkward to use in the extreme, and the far more reasonable Panasonic S1 II. The Panasonic S1 II is easily the most capable and well-suited L-mount camera for sports and action, and it has a sophisticated autofocusing system that can be configured for a given situation. The Sigma BF, on the other hand, has a very simple setup, with basic human and animal detection modes, and no way to alter AF behavior or response.

A man in an orange shirt kneels outdoors on dry grass, adjusting a camera with a large lens. A small, blurred dog walks by in the background. — The Panasonic S1 II is a wonderful camera with great controls.

I wanted to try the autofocus out on some wildlife in the area, but the predictability of finding animals this time of year is tricky. Then I remembered that I have a dog, so it was off to the local dog park to get some running tests. My dog, Penny, is quite small and blends in with the warm-tone grasses in the area, so the test should be quite challenging. Jordan Drake also offered to provide us with one of his now-famous running tests, which would certainly give us a good human target to test as well.

Buy the Sigma 300-600mm f/4 DG OS Sports new on B&H Buy the Sigma 300-600mm f/4 DG OS Sports used on KEH.com

The Panasonic S1 II Tests

Let’s start the testing with the Panasonic S1 II. I configured the camera to acquire and track a subject in the most locked-on fashion. Panasonic has a decent autofocusing system, but I don’t find the hit rate to compete with the “big three” manufacturers in Sony, Canon, and Nikon. That being said, the 24-megapixel stacked sensor and hybrid phase-detect AF in the S1 II are capable of tracking fast-moving subjects.

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The shots of Penny started in focus, with clear depictions of the eye detection at work. I shot rapid sequences at five and eight frames per second, and found the results to be fairly consistent.

A man outdoors in a red shirt and gray jacket is captured mid-motion, running with his arm bent in front of his face and an intense expression. The background is blurred, with wooden fences and dry grass visible. — The Panasonic S1 II makes easy work of a Jordan running test.

A man with a backpack runs outdoors, clenching his fists and yelling with an intense, angry expression. The background is blurred, showing bare trees and a field. — There was no issue with consistency on the portrait tests.

A brown curly-haired dog runs through a dry grassy field with its ears flapping and tongue out, wearing a patterned collar. A blurred wooden fence is visible in the background. — The ability of the S1 II to customize AF response is an important benefit.

The tests of Penny proved to be difficult for the camera, with erratic movement and changes in speed causing some missed frames to happen. However, the S1 II was usually able to require focus within a few frames and keep tracking. It never lost focus by switching to the background instead, and the human results were very consistent. Most importantly, the results were predictable over multiple tests, and I could tweak responsiveness settings and focus area modes to suit different scenarios.

Let’s also remember that the S1 II provides an excellent EVF to follow along with the action, and the grip and weight are well-suited to the larger telephoto lens. Clearly, the S1 II is solid tool for the job.

A girl in casual clothes throws a ball with a blue launcher while a brown dog excitedly runs ahead in a grassy field. Trees and a wooden fence are blurred in the background. — My daughter was happy to assist in our wildlife tests.

A small, curly-haired brown dog runs joyfully across a dry grassy field, its ears flapping and mouth open with a ball inside. The background is blurred, suggesting motion and an outdoor setting. — The S1 II was far from perfect and sometimes misfocussed slightly.

A curly-haired dog runs energetically across a grassy field while a person in the background, holding a blue stick, plays with another dog. The scene is outdoors with a wooden fence and trees visible. — The S1 II was just a little more accurate overall.

The Sigma BF Tests

On to the meat of what we wanted to test. The Sigma BF only allows for a few autofocus area options and, in particular, it was the single point tracking that most impressed me when I first reviewed the camera. The Sigma would effortlessly lock on to any object and follow it continuously throughout the frame. This was great for focusing, recomposing, and also changing distance, and gave me a confidence-inspiring experience.

It honestly reminded me of the amazing Real-Time tracking of the Sony cameras, and was so successful to use that it inspired us to wonder about this crazy experiment in the first place.

A man with gray hair is adjusting a large white telephoto camera lens outdoors, with dry grass visible in the background. — The Sigma BF is not an ideal choice on the back of a huge telephoto lens.

A man with a tense expression is running outdoors. He wears a red shirt and blue jacket, with his arms bent and fists clenched. The background is blurred with bare trees and a fence. — Jordan gives it his all when it comes to running tests.

A man wearing a red shirt and gray jacket is running outdoors with a determined expression. The background is blurred, showing trees and a fence. — The Sigma BF only lost focus once or twice during a running test.

However, I did start to see the cracks when putting the system up against a more difficult scenario: my erratic moving dog. The Sigma BF acquired eye detection on Penny very easily, and would instantly switch to body detection if needed. It would certainly handle a few shots in a row without issue, but would often lose the subject when a quick direction change happened.

On some runs, the hit rate would rival the Panasonic results, but only when Penny ran directly towards the camera. Often, it would lose focus at similar times to the Panasonic but would have more difficulty reacquiring the dog.

It did a much better job with Jordan, though, and tracked him running with only a few missed frames. Perhaps people are easier to track because of the extra contrast and cleaner backdrop, because both cameras were far more successful in this test. I think that the BF also struggles with getting focus right on the target. Often, the subject focus would be close, but also slightly behind the subject.

A small, fluffy brown dog with a blue harness runs energetically through a dry, grassy field, tongue out and ears flapping in the wind. — The Sigma BF would often be just behind the point of focus.

A small brown dog runs through dry grass toward a yellow ball, while a person in the background uses a blue ball launcher. — When Penny was running predictably, the BF did a fine job.

A child in light blue pants stands behind a small brown dog running through a dry grassy field. The child's upper body is out of frame, and a wooden fence runs across the background. — The Sigma BF would sometimes drift to the background.

A small brown dog wearing a green harness runs through a dry grassy field, excitedly chasing a yellow ball that has just been thrown. The background is blurred, with a fence faintly visible. — I wasn’t expecting much from the Sigma BF, but it does show at least some potential.

Future Potential

The most telling part of this experiment was the fact that the Sigma BF begins with such a strong base going forward. I think it has a lot of potential as a starting point for future developments, and Sigma’s CEO has said he has an interest in making a more serious professional-level body to make use of its longer telephoto lenses.

The current system has no issue with casual photography, portraits, and street or travel photography. If Sigma can add meaningful updates to its animal-detection algorithms and a way to customize the autofocusing for more specific shooting scenarios, I think it will have a strong contender for more demanding photography, and could even put serious pressure on Panasonic to improve its focusing technology.